1. Field of the Invention
The present invention relates to a radiation image information recording and reading apparatus having two recording units, which records radiation-transmitted image of an object placed on one selected from the two recording units on a stimulable phosphor sheet as radiation image information and reads the radiation image information from the sheet so as to produce an image signal.
2. Description of the Related Art
There has recently been proposed a radiation image information recording and reading apparatus of a type wherein radiation image information of an object such as a human body is first stored and recorded on a stimulable phosphor sheet using a stimulable phosphor and the stimulable phosphor sheet is then scanned with stimulating rays to emit accelerated light therefrom, thereby photoelectrically detecting the emitted light so as to produce an image information signal. When the image information signal produced by the apparatus is electrically processed to generate a radiation image of the object appropriate to the diagnosis, a final image may be reproduced as a hard copy or may be reproduced as a visible image on a CRT.
In the radiation image information recording and reading apparatus referred to above, it is unnecessary to semipermanently record the radiation image information on the stimulable phosphor sheet. The stimulable phosphor sheet is used to temporarily bear image information thereon with a view toward recording an image on the above final recording medium. Therefore, stimulable phosphor sheet may repeatedly be used, and hence the repetitive use of the stimulable phosphor sheet can provide considerable economy. Incidentally, the reuse of the stimulable phosphor sheet is made in the following manner. That is, the energy of radiation, which remains on the stimulable phosphor sheet from which the accelerated light has already been read, is discharged or radiated by a method described in U.S. Pat. No. 4,400,619 and Japanese Patent Application Laid-Open No. 56-12599 for example so as to erase the remaining or residual radiation image information from the sheet. Thereafter, such a stimulable phosphor sheet may be used again for the recording of the radiation image information thereon.
From the above standpoint, there has been proposed a radiation image information recording and reading apparatus comprising a recording unit for recording radiation image information of an object on a stimulable phosphor sheet, a reading unit for reading the radiation image information stored and recorded on the stimulable phosphor sheet, and an erasing unit for radiating the radiation energy remaining on the sheet from which the radiation image information has already been read (see Japanese Patent Application Laid-Open No. 60-256134 and U.S. Pat. No. 4,851,679).
In this type of apparatus, an object is normally placed on a movable exposure or radiation-photography table in a recumbent state and the table is then moved to set a part of the object to be radiographed to the most suitable position, followed by making of radiographs of the affected parts of the head, chest, abdomen, etc. of the object. In this case, radiation emitted from a radiation source passes through the object, the table and a scattered-radiation removing grid so as to reach a stimulable phosphor sheet. Thus, the radiation is absorbed by the table and the scattered-radiation removing grid and hence the radiation dose is reduced correspondingly, thereby developing inconvenience such as deterioration in the quality of an image. Therefore, the radiation photography of the object is made while the dose of the radiation emitted from the radiation source is being increased.
On the other hand, when it is desired to make radiographs of the bones of the object's limbs, i.e., human hand and feet, for example, the area of the object to be radiographed is relatively narrow and the object is relatively thin in cross-section. It is therefore unnecessary to use the movable radiation-photography table and the scattered-radiation removing grid. Accordingly, the radiation photography of the object is normally made by a radiation image information recording and reading apparatus using a cassette with a stimulable phosphor sheet stored therein.
In the conventional method, one of radiation image information recording and reading apparatuses should be selected according to the parts of the object to be radiographed and the respective apparatuses should separately be provided. Therefore, a problem in space for each of the apparatuses to be installed as well as a problem in cost takes place. In general, a single radiation image information recording and reading apparatus constructed in such a manner that the movable radiation-photography table and the scattered-radiation removing grid can be loaded and unloaded in and from the apparatus cannot provide suitable radiation photography associated with various parts of an object to be subjected to radiation photography.